Ever since the first image of an object was captured on film, a serious problem was apparent which has continued to plague the field of image capture and reproduction to the present day, namely imperfections in the recording medium itself which distort and obscure the original image sought to be captured. These imperfections occur in innumerable forms including dust, scratches, fingerprints, smudges and the like. Archival polypropylene sleeves employed to protect negatives even contribute to the problem by leaving hairline surface scratches as the negatives are pulled out of and replaced into the sleeves.
The problem is even worse with such negatives than with transparencies, first because viewing the negative requires a gamma, or ratio gain, of more than two, and secondly because filmstrips are more subject to contact than are mounted transparencies. Such imperfections may be found present even in fresh photographic film in surface waves, and may further arise from improper processing causing mild reticulation, and unbleached silver for example. Not only are such non-image imperfections surface related but can even be caused for example by microbubbles in emulsion within the film itself.
Numerous measures have been developed in the art in an attempt to address the problem, particularly with respect to captured high resolution images. One approach has been that of prevention as for example, in the development process itself. Expensive anti-static equipment including spray machines to neutralize dust-attracting charges are employed for example by reputable photo finishers. Photo finishers also attempted to employ diffuse light source enlargers that helped reduce the effects of refraction of the light by imperfections in the photo finishing processes.
Yet another way the problem was approached sought to minimize the effects of these imperfections once they were present by various correction techniques, most of which were manual and thus highly labor-intensive and expensive. As an example, during the photo finishing process, a highly trained individual might spend a great deal of time with various spotting dyes and an extremely small spotting brush seeking to essentially paint out the imperfections. Another technique was to wipe on or immerse the negatives in a light oil in an attempt to optically fill scratches.
The problem of dust, scratches and the like in large measure contributed to the decline in use and popularity of vinyl records. The film industry has been concerned that the problem may in like manner jeopardize the long term future of analog images. Notwithstanding the significant efforts that were made to solve the problem it seemed that no matter what was done the problem nevertheless persists. This is particularly with respect to enlargements and high resolution scans. Thus the problem is becoming even more acute and recognized as resolution increases and multimedia brings attention to it with the increase in film scanning for computer applications.
As the art developed, various attempts were made to automate the correction process, particularly with respect to digital image systems. In such systems once an imperfection was detected, various "fill" algorithms had been developed for correcting the image at the situs of the imperfection. Nevertheless, heuristics or human intervention were required to detect the imperfections with a subjective threshold. Typically the identified area to be corrected in this manner was much larger than necessary under the present invention, in part due to these subjective criteria for detecting defective areas.
Automated methods were in fact developed for even detecting imperfect areas in recording media, notably as described in the German patent #2821868.0, published Nov. 22, 1979, entitled "Method and Device for Detecting Recording and Counting of Mechanical Damage to Moving Bands, for Example Films". In this system, a source of infrared energy impinged upon the film medium. A scanned infrared image thereafter was taken of the film in question by sensors detecting reflection of the infrared energy from the film surface. However several limitations were present in this system.
First, its purpose was not to correct an image present on the film for the effects of such detected film defects. Rather the system was implemented simply to monitor the prevalence of these defects in an automated photographic development process whereby, for example, the process could be automatically shut down if the defect rate exceeded a prescribed level. Moreover, infrared image was not recorded in registry with any other images from the visual portion of the electromagnetic spectrum. This alone would render it extremely difficult to subtract out the effect of such imperfections noted in the IR image from similar defects present and visible in the visual record of the image. On the contrary, the optical IR path was a reflective one from the IR source to sensor different from the other sensors unutilized for image processing.
Such systems have in fact been developed for capturing images of objects along an identical optical path wherein each such image corresponds to a different portion of the electromagnetic spectrum, notably in the satellite photography and reconnaissance arts, for example, for purposes of image enhancement. In such systems, images of one spectrum may thus be superimposed on those from another spectrum of the identical object whereupon various image processing algorithms well known in the art might thereafter be employed. For example, an infrared mapping system might functionally relate the IR spectrum of carbon dioxide in an earth surface image from that of another portion of the spectrum to draw conclusions regarding surface vegetation or the like as, for example, in crop inventorying and such techniques have been well developed. However, these systems while in some sense enhancing the captured image, are not detecting through means of the infrared spectrum defects and imperfections associated with the recording medium itself, and thereafter using such information to enhance the image stored on the medium.
From the foregoing, an object of the invention is to automatically render invisible or substantially reduce the effect of physical imperfections of the storage medium such as as dust scratches, and the like, from the desired image stored on the film to be perceived. It is a further object of the invention to precisely detect boundaries of recording medium imperfections.